Arnaud Norena

Psychoacoustic characterization of the tinnitus spectrum: implications for the underlying mechanisms of tinnitus.

In this study, an original psychometric procedure was used in order to characterize in more detail than in previous studies the different perceptual components of tinnitus, i.e. auditory sensations which are perceived in the absence of a corresponding external acoustic stimulus. Ten subjects with chronic tinnitus were asked to rate on a numeric scale the contribution of elementary pitch sensations evoked by isolated frequency components to their overall tinnitus sensation. The resulting ‘internal tinnitus spectra’, which represented the estimated perceptual contribution to the tinnitus sensation as a function of frequency over a large range of frequencies, were found to occupy a wide frequency range corresponding largely to that at which hearing thresholds were abnormally elevated. In most cases, they exhibited a broad peak falling within the hearing loss range. This pattern of result suggests that in subjects with high-frequency hearing loss, tinnitus sensations, when present, resemble those evoked by high-frequency noise bands with, in some cases, a superimposed tonal-like pitch. These results confirm and extend earlier results in the literature and agree with the patients’ reports; their practical implications for the design of future studies on tinnitus and theoretical implications for the understanding of the neurophysiological mechanisms underlying tinnitus are discussed. The results of an additional experiment showed that the internal tinnitus spectrum could be altered by perceptual training in a fine frequency discrimination task with tones in the frequency range of the main peak of the tinnitus spectrum.

High-frequency tinnitus without hearing loss does not mean absence of deafferentation

A broad consensus within the neuroscience of tinnitus holds that this audiologic condition is triggered by central deafferentation, mostly due to cochlear damage. The absence of audiometrically detectable hearing loss however poses a challenge to this rather generalizing assumption. The aim of this study was therefore to scrutinize cochlear functioning in a sample of tinnitus subjects audiometrically matched to a normal hearing control group. Two tests were applied: the Threshold Equalizing Noise (TEN) test and a pitch scaling task. To perform well on both tasks relatively normal functioning of inner hair cells is a requirement. In the TEN test the tinnitus group revealed a circumscribed increment of thresholds partially overlapping with the tinnitus spectrum. Abnormal slopes were observed in the pitch scaling task which indicated that tinnitus subjects, when presented with a high-frequency stimulus, relied heavily on input derived from lower-frequency inner hair cells (off-frequency listening). In total both results argue for the presence of a deafferentation also in tinnitus subjects with audiometrically normal thresholds and therefore favour the deafferentation assumption posed by most neuroscientific theories.

Spectrally enhanced acoustic environment disrupts frequency representation in cat auditory cortex

Sensory environments are known to shape nervous system organization. Here we show that passive long-term exposure to a spectrally enhanced acoustic environment (EAE) causes reorganization of the tonotopic map in juvenile cat auditory cortex without inducing any hearing loss. The EAE consisted of tone pips of 32 different frequencies (5–20 kHz), presented in random order at an average rate of 96 Hz. The EAE caused a strong reduction of the representation of EAE frequencies and an over-representation of frequencies neighboring those of the EAE. This is in sharp contrast with earlier developmental studies showing an enlargement of the cortical representation of EAEs consisting of a narrow frequency band. We observed fewer than normal appropriately tuned short-latency responses to EAE frequencies, together with more common long-latency responses tuned to EAE-neighboring frequencies.

Tinnitus-related neural activity: theories of generation, propagation, and centralization.

The neuroscience of tinnitus represents an ideal model to explore central issues in brain functioning such as the formation of auditory percepts, in addition to opening up new treatment avenues for the condition in the long-term. The present review discusses the origin and nature of tinnitus-related neural activity. First, we review evidence for the hypothesis that tinnitus is caused by the central nervous system changes induced by sensory deprivation, even when hearing loss is not visible in the audiogram. Second, we suggest that changes in neural activity in individual central structures may not be sufficient to underlie the tinnitus percept. Instead, we propose that tinnitus may arise from functional alterations at multiple levels which promote abnormal propagation of neural activity throughout the network involved in auditory perception. In this context, functional coupling within and between central auditory structures may be especially important to consider. Investigating how sensory deprivation affects functional coupling between areas, which might be reflected in changes in temporal coherence of intrinsic ongoing activity patterns, may give critical insights into the mechanisms of tinnitus.

Effects of hearing aid fitting on the perceptual characteristics of tinnitus.

Restoration of auditory input through the use of hearing aids has been proposed as a potentially important means of altering tinnitus among those tinnitus sufferers who experience significant sensorineural hearing loss. In animal models of neural plasticity induced by noise trauma, high-frequency stimulation in deafferented regions of the auditory spectrum has been shown to modulate cortical reorganization after hearing loss, a result which suggests that the neural basis of tinnitus is subject to interference by acoustic stimulation. This study drew on deafferentation models to investigate the effect of hearing aids on the psychoacoustic properties of the tinnitus sensation, using both conventional amplification and high-bandwidth amplification regimes. The tinnitus percept was affected only weakly in the conventional amplification group, and was not at all affected in the high-bandwidth group. The changes observed under conventional, low-to-medium frequency amplification may indicate that the perceptual characteristics of tinnitus depend on the pattern of sensory inputs - notably a contrast in activity between adjacent central auditory regions of more and less afferent activity - while the absence of modifications in the high-bandwidth amplification group suggests limit on the tractability of the tinnitus percept. This limit to the malleability of the tinnitus percept may arise from either the extent of hearing deficits or the duration and robustness of the neuroplastic changes that originally give rise to tinnitus.

An auditory negative after-image as a human model of tinnitus

The Zwicker tone (ZT) is an auditory after-image, i.e. a tonal sensation that occurs following the presentation of notched noise. In the present study, the hypothesis that neural lateral inhibition is involved in the generation of this auditory illusion was investigated in humans through differences in perceptual detection thresholds measured following broadband noise, notched noise, and low-pass noise stimulation. The detection thresholds were measured using probe tones at several frequencies, within as well as outside the suppressed frequency range of the notched noise, and below as well as above the corner frequency of the low-pass noise. Thresholds measured after broadband noise using a sequence of four 130-ms probe tones (with a 130-ms inter-burst interval) proved to be significantly smaller that those measured using the same probe tones after notched noise at frequencies falling within the notch, but larger for frequencies on the outer edges of the noise. Thresholds measured following low-pass noise using the same sequence of probe tones were found to be smaller at frequencies slightly above the corner, but larger at lower, neighboring frequencies. This pattern of results is consistent with the hypothesis that the changes in auditory sensitivity induced by stimuli containing sharp spectral contrasts reflect lateral inhibition processes in the auditory system. The potential implications of these findings for the understanding of the mechanisms underlying the generation of auditory illusions like the ZT or tinnitus are discussed.

Different Teams, Same Conclusions? A Systematic Review of Existing Clinical Guidelines for the Assessment and Treatment of Tinnitus in Adults

Background: Though clinical guidelines for assessment and treatment of chronic subjective tinnitus do exist, a comprehensive review of those guidelines has not been performed. The objective of this review was to identify current clinical guidelines, and compare their recommendations for the assessment and treatment of subjective tinnitus in adults. Method: We systematically searched a range of sources for clinical guidelines (as defined by the Institute of Medicine, United States) for the assessment and/or treatment of subjective tinnitus in adults. No restrictions on language or year of publication were applied to guidelines. Results: Clinical guidelines from Denmark, Germany, Sweden, The Netherlands, and the United States were included in the review. There was a high level of consistency across the guidelines with regard to recommendations for audiometric assessment, physical examination, use of a validated questionnaire(s) to assess tinnitus related distress, and referral to a psychologist when required. Cognitive behavioral treatment for tinnitus related distress, use of hearing aids in instances of hearing loss and recommendations against the use of medicines were consistent across the included guidelines. Differences between the guidelines centered on the use of imaging in assessment procedures and sound therapy as a form of treatment for tinnitus distress respectively. Conclusion: Given the level of commonality across tinnitus guidelines from different countries the development of a European guideline for the assessment and treatment of subjective tinnitus in adults seems feasible. This guideline would have the potential to benefit the large number of clinicians in countries where clinical guidelines do not yet exist, and would support standardization of treatment for patients across Europe.

Membrane potential dynamics of populations of cortical neurons during auditory streaming.

How a mixture of acoustic sources is perceptually organized into discrete auditory objects remains unclear. One current hypothesis postulates that perceptual segregation of different sources is related to the spatiotemporal separation of cortical responses induced by each acoustic source or stream. In the present study, the dynamics of subthreshold membrane potential activity were measured across the entire tonotopic axis of the rodent primary auditory cortex during the auditory streaming paradigm using voltage-sensitive dye imaging. Consistent with the proposed hypothesis, we observed enhanced spatiotemporal segregation of cortical responses to alternating tone sequences as their frequency separation or presentation rate was increased, both manipulations known to promote stream segregation. However, across most streaming paradigm conditions tested, a substantial cortical region maintaining a response to both tones coexisted with more peripheral cortical regions responding more selectively to one of them. We propose that these coexisting subthreshold representation types could provide neural substrates to support the flexible switching between the integrated and segregated streaming percepts.

Loudness changes associated with the perception of an auditory after-image

The Zwicker tone (ZT) is an auditory sensation that occurs following the presentation of broadband noise containing a spectral notch. The present study aimed to test whether the changes in auditory thresholds that have been shown to follow the presentation of the ZT inducer are accompanied by suprathreshold effects. Using an interaural loudness-balance procedure, the loudness of probe tones presented after notched and after flat noise was compared. The results revealed small differences in the influence of the two types of noise on loudness at low intensities only. This suggests that the influence of notched noise stimulation on the auditory system is mediated by changes in the internal noise in auditory centres.

Auditory Brainstem Responses in Tinnitus: A Review of Who, How, and What?

The auditory brainstem response (ABR) in tinnitus subjects has been extensively investigated over the last decade with the hopes of finding possible abnormalities related to the pathology. Despite this effort, the use of the ABR for tinnitus diagnosis or as an outcome measure is under debate. The present study reviewed published literature on ABR and tinnitus. The authors searched PubMed, MedLine, Embase, PsycINFO, and CINAHL, and identified additional records through manually searching reference lists and gray literature. There were 4,566 articles identified through database searching and 151 additional studies through the manual search (4,717 total): 2,128 articles were removed as duplicates, and 2,567 records did not meet eligibility criteria. From the final 22 articles that were included, ABR results from 1,240 tinnitus subjects and 664 control subjects were compiled and summarized with a focus on three main areas: the participant characteristics, the methodology used, and the outcome measures of amplitude and/or latency of waves I, III, and V. The results indicate a high level of heterogeneity between the studies for all the assessed areas. Amplitude and latency differences between tinnitus and controls were not consistent between studies. Nevertheless, the longer latency and reduced amplitude of wave I for the tinnitus group with normal hearing compared to matched controls was the most consistent finding across studies. These results support the need for greater stratification of the tinnitus population and the importance of a standardized ABR method to make comparisons between studies possible.